The present invention relates to optical digital data storage devices and to deformable membrane reflectors for use in the optical systems of those devices.
In a conventional optical data storage device, such as an audio compact disk (CD) player or an optical read-only memory (OROM), an objective lens focusses laser light onto the surface of an optical storage medium and collects light reflected from the medium. Other forms of conventional optical data storage devices employ secondary collecting lenses to collect laser light transmitted by the storage medium. The objective lens (and/or the secondary lens) is usually mounted on a voice-coil actuator so that the lens's longitudinal position relative to the storage medium, which is often a coated plastic disc, can be rapidly and accurately controlled. As data storage capacities increase, the performance requirements of the opto-mechanical systems of data storage devices become increasingly difficult to achieve. A device which has not previously been applied to the focus control problems of optical data storage devices is the deformable membrane reflector, the basic form of which has been described previously in several U.S. patents.
The patent to Jones, U.S. Pat. No. 3,322,483, discloses a metallized membrane which is electrostatically deformed into selectable surface profiles for use as an astronomical reflector. Spherical, elliptical and other shapes are obtained by varying the shape of an electrode or the nature of an electric signal applied to the electrode. The patent to Evans, U.S. Pat. No. 2,403,915, also discloses a metallized membrane which is deformed electrostatically into the shape of an opposed electrode. The shape of the reflector can be rapidly modulated and can assume other than a spherical profile.
The patent to Mueller, U.S. Pat. No. 1,906,803, and to Jenkins, U.S. Pat. No. 1,525,550, also disclose deformable mirrors which vary the focal position of ray bundles they reflect. Mueller causes the intensity of light passing a variably shaped beam-stop to be modulated by small deflections created by the deformable mirror. Jenkins varies the convergence characteristics of a light beam reflected from a mirror attached to a metal surface that is deformed by the influence of an electromagnet in a system for receiving pictures by radio.
None of these prior issued patents suggest the use of a membrane reflector in an optical data storage device, nor do they disclose mirrors which could be so used. The sizes and weights of the mirrors taught are impractically large for devices which today encompass a mere few tens of cubic centimeters.
Thus, it is an object of the present invention to provide a method of focus control which provides accurate and rapid adjustment of the optical system of an optical data storage device without requiring an excessively large volume. Other objects and advantages of the present invention will become apparent after a reading of the following detailed description and drawings.